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Net-Zero Communities Sprout in New York

Tired of conventional construction, a Hudson River Valley builder turns to insulating concrete forms and airtight building envelopes

Posted on Aug 27 2013 by Scott Gibson

Anthony Aebi lost his appetite for conventional construction in 2006. Working on his own house, he was discouraged by the quality of the construction details he saw. He says that he realized that, in the grand scheme of things, the house probably wasn’t going to last that long.

“I realized the conventional way we build houses, they’re temporary,” the upstate New York builder said recently by telephone. “They don’t have life spans over 60 years, pretty much. As I was building I could already see decomposition occurring and I thought I was going to quit building, because I didn’t want to build crap any more, or look into other ways of doing things.”

His solution was to start building with insulated concrete forms (ICFs), which combine expanded polystyrene (EPSExpanded polystyrene. Type of rigid foam insulation that, unlike extruded polystyrene (XPS), does not contain ozone-depleting HCFCs. EPS frequently has a high recycled content. Its vapor permeability is higher and its R-value lower than XPS insulation. EPS insulation is classified by type: Type I is lowest in density and strength and Type X is highest.) foam insulation with a core of reinforced concrete. His houses have triple-pane windows, spray polyurethane foam in the roof, ground-source heat pumps for heating and cooling, and rooftop photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. arrays for power. They’re all designed for net-zero energyProducing as much energy on an annual basis as one consumes on site, usually with renewable energy sources such as photovoltaics or small-scale wind turbines. performance.

Aebi’s construction company, Greenhill Contracting Inc., is working on or planning three net-zero subdivisions within a 20-mile radius of New Paltz, New York, some 80 miles north or New York City in the Hudson River Valley. Another two-house project in Esopus, New York, has been completed. When fully built out, the projects will have a total of 47 houses ranging in size from about 2,000 s.f. to 6,000 s.f.

ICFs, from footings to roof

Although the houses vary in size and architectural design, they do have one thing in common: the exterior walls, “from the footers to the roof, including the gables,” are made of ICFs manufactured by Fox Blocks.

A 6-inch core of concrete is sandwiched between two 2 5/8-inch layers of EPS insulation, giving the wall a total R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. of about 22, Aebi says. There are between 3 1/2 inches and 4 1/2 inches of closed-cell sprayed polyurethane under the slab, and R-60 worth of sprayed foam in the roof.

Although the R-values of the exterior walls aren’t that high when compared with many net-zero or PassivhausA residential building construction standard requiring very low levels of air leakage, very high levels of insulation, and windows with a very low U-factor. Developed in the early 1990s by Bo Adamson and Wolfgang Feist, the standard is now promoted by the Passivhaus Institut in Darmstadt, Germany. To meet the standard, a home must have an infiltration rate no greater than 0.60 AC/H @ 50 pascals, a maximum annual heating energy use of 15 kWh per square meter (4,755 Btu per square foot), a maximum annual cooling energy use of 15 kWh per square meter (1.39 kWh per square foot), and maximum source energy use for all purposes of 120 kWh per square meter (11.1 kWh per square foot). The standard recommends, but does not require, a maximum design heating load of 10 W per square meter and windows with a maximum U-factor of 0.14. The Passivhaus standard was developed for buildings in central and northern Europe; efforts are underway to clarify the best techniques to achieve the standard for buildings in hot climates. designs, air infiltration rates are very low.

Aebi said three houses in a subdivision called The Preserve at Mountain Vista were just blower-door tested with leakage measured at 0.29, 0.28 and 0.34 air changes per house at 50 pascals of pressure (ach50). That’s about half the air leakage of the Passivhaus standard, 0.6 ach50.

Abe's houses also have Lifebreath heat-recovery ventilators, triple-glazed windows with U-factors of roughly 0.20, and, most recently, ground-source heat pumps manufactured by Water Furnace. The homes' PVPhotovoltaics. Generation of electricity directly from sunlight. A photovoltaic (PV) cell has no moving parts; electrons are energized by sunlight and result in current flow. arrays are rated at 7 kW to 15 kW, depending on the size of the house.

In all, Aebi says he has completed nine houses, seven of which have measured net-zero performance for at least one year.

Bringing net-zero to production building

The largest of the company’s projects is Green Acres, a 25-unit subdivision where seven houses have been completed so far. The first was occupied in March 2009.

Aebi’s current project is the nine-unit Mountain Vista subdivision, which he plans to complete before returning to Green Acres or the planned Scenic Meadows subdivision. All nine shells at Mountain Vista are up and windows installed.

Mountain Vista is an attempt to lower the price of these net-zero houses by 20% to 30% when compared with a typical one-off custom house.

“The idea is that we’re using production techniques to try to get the prices down,” he said. “By building nine at a time we’re getting the economies of scale. We're sticking our necks out a little bit but the idea is what a production builder would typically do.”

The houses average 2,400 s.f. in size and will sell in the “low to mid 400s,” according to Aebi. Once land, septic, infrastructure and other non-house expenses are backed out, he hopes to get construction costs down to $100 per s.f. or less.

Hoping for a hand from Washington

State and federal incentives help reduce the upfront cost of energy systems and heating and cooling in the houses that Aebi is building, but he also is banking on a new measure introduced in the U.S. Senate in June.

The SAVE Act, introduced by Sen. Michael Bennett, a Colorado Democrat, would make it easier for borrowers to get credit for the energy-saving features built into the house. A lack of clear appraisal guidelines that allow realistic valuations for energy efficiency has been a frustration for many builders and homeowners.

The measure has been referred to the Senate Banking, Housing and Urban Affairs Committee, but so far there’s been no further progress.

How Greenhill’s projects ultimately do may depend on convincing buyers they’ll get a good deal even if the initial costs for net-zero construction are higher. And Aebi thinks the legislation is key. “If that bill passed it would make it completely foolhardy not to build or buy a non-zero energy house,” he said.


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Image Credits:

  1. Greenhill Contracting Inc.

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